The invention relates, in general, to a method and apparatus for weighing objects and, in particular, to a system for determining the weight of each object in a succession of moving objects.
The present invention relates to a method for automatically weighing moving objects that either are self-propelled (such as a driven automobile or carriage) or moved by a conveyor system. In the past, systems for weighing moving objects used two trigger signals to control the weighing process. One trigger signal was used to start the weighing process, and the other trigger signal was used to complete the weighing process. The measurements made during the period of time between the two signals could then be processed in different ways to, for example, obtain an average weight or determine the stability of conditions within the system. Other known systems use only one trigger signal to cause a single measurement to be made, providing an instantaneous value of a weight or force for determining the stability of conditions.
This invention further concerns a weighing algorithm used in automatic weighing devices with data registration for a moving object. Most electronic scale algorithms for calculating weight provide statistical approximations of actual weight 25 signals. The latest digital signal is compared with a predetermined range, and if within the range, the last digital weight signal will be added to the statistical approximation. A zero storage register stores the zero weight. See generally U.S. Pat. No. 4,241,407. Some electronic weight measuring devices use two memory buffers and a data weight generator. The first memory buffer is used for data processing. The second buffer is used for storing and processing zero point data. See, for example, U.S. Pat. No. 4,774,683.
Another method automatically zero balances an electronic scale. If an average of input signals show that zero is within predetermined limits, the system displays xe2x80x9cScale Readyxe2x80x9d; if not, it displays blank. Zero is calculated by dividing the sum of the readings by the number of readings; see U.S. Pat. No. 4,751,661.
As noted above, dynamic weighing algorithms use two trigger signals to control the start and the stop of the weighing process. The measurements between start and stop are then processed in different ways (average calculation, stability conditions, etc.) Some algorithms use just one signal to load an instant measured value or to check stability conditions. All of these algorithms also control the flow of material on the scale. This means that logic will be added to software to regulate the flow of objects to be weighed on the line, and this logic can create interfacing problems and reduce the throughput. Therefore, a need remains for a method and apparatus which simplifies the interface circuitry required for operating a system for weighing moving objects using a series of measurements without the need to slow or stop the object for weighing purposes.
The present invention provides an improved apparatus for weighing moving objects and in particular an improved system for automatically weighing moving objects that either are being self-propelled or being moved by a conveyor system. According to one aspect of the invention, an apparatus for measuring the weight of a moving object includes a scale platform for supporting the moving object to be weighed, one or more force sensors for determining the force applied to the scale platform by the moving object, a numeric computing device which continuously samples and stores the values determined by the force sensors, and only one sensor for activating a signal used to trigger the numeric computing device. The sampling rate by which the numeric computing device samples and stores force sensors is sufficient to ensure a succession of samples during the time the object to be weighed has been supported by the scale platform. The sensor for activating the trigger signal detects the leading edge of the moving object and activates the trigger signal which causes the numeric computing device to calculate the weight of the moving object based on the stored succession of samples (last xe2x80x9cMxe2x80x9d samples).
The invention also provides a method of weighing a moving object in which the object to be weighed either is moved or moves across a weighing platform as a weight sensor continuously senses the load or force applied to the scale. The output of the weight sensor is sampled at a rate sufficient to ensure that a succession of samples is taken during the period in which the object is on the platform. The sampled values are stored in a memory unit or buffer.
A sensor signals when the moving object has reached the end of the scale conveyor (assuring that the moving object has been supported by the scale for a period of time sufficient to ensure that the succession of samples has been stored) at which time the weight of the object is calculated based upon the succession of stored sample values. In one embodiment, the sampling and storing steps are repeated continuously and the samples are stored in a buffer on a first-in, first-out basis, enabling calculation of the weight of the object based upon a recorded series of xe2x80x9cMxe2x80x9d samples measured just prior to the object moving into the detection path of sensor.
In one embodiment, the weighing process is controlled so that the number of samples is determined by the relationship: M=(Lsxe2x88x92Lo)/(Vo*Tcy); where Ls is the length of the platform in the direction of travel of the object, Lo is the maximum length of objects to be weighed, Vo is the maximum velocity at which objects move over the platform, and Tcy is a period of time between samples. Preferably M is at least as great as a predetermined number of samples used by the processor to calculate the weight of the object. It is also preferable that the objects move or are moved across the weighing platform or scale at a substantially uniform speed and that the spacing between objects is controlled to ensure that one object at a time is weighed.